Bug 1786306 de-virtualize some methods that are not overridden r=pehrsons

These might not have been overridden since
https://hg.mozilla.org/mozilla-central/rev/09943651fa85#l15.50 and
https://hg.mozilla.org/mozilla-central/rev/9d11ad3a0bf4#l2.89

Depends on D158303

Differential Revision: https://phabricator.services.mozilla.com/D158304

dom/media/MediaTrackGraph.h

@@ -268,16 +268,16 @@ class MediaTrack : public mozilla::LinkedListElement<MediaTrack> {
   void SetGraphImpl(MediaTrackGraph* aGraph);
 
   // Control API.
-  virtual void AddAudioOutput(void* aKey);
-  virtual void SetAudioOutputVolume(void* aKey, float aVolume);
-  virtual void RemoveAudioOutput(void* aKey);
+  void AddAudioOutput(void* aKey);
+  void SetAudioOutputVolume(void* aKey, float aVolume);
+  void RemoveAudioOutput(void* aKey);
   // Explicitly suspend. Useful for example if a media element is pausing
   // and we need to stop its track emitting its buffered data. As soon as the
   // Suspend message reaches the graph, the track stops processing. It
   // ignores its inputs and produces silence/no video until Resumed. Its
   // current time does not advance.
-  virtual void Suspend();
-  virtual void Resume();
+  void Suspend();
+  void Resume();
   // Events will be dispatched by calling methods of aListener.
   virtual void AddListener(MediaTrackListener* aListener);
   virtual RefPtr<GenericPromise> RemoveListener(MediaTrackListener* aListener);
@@ -289,7 +289,7 @@ class MediaTrack : public mozilla::LinkedListElement<MediaTrack> {
    * Note that the listener will be notified on the MediaTrackGraph thread
    * with whether the installation of it at the source was successful or not.
    */
-  virtual void AddDirectListener(DirectMediaTrackListener* aListener);
+  void AddDirectListener(DirectMediaTrackListener* aListener);
 
   /**
    * Removes aListener from the source track of this track.
@@ -298,7 +298,7 @@ class MediaTrack : public mozilla::LinkedListElement<MediaTrack> {
    * about this, removing when the source cannot be found, or when the listener
    * had already been removed does nothing.
    */
-  virtual void RemoveDirectListener(DirectMediaTrackListener* aListener);
+  void RemoveDirectListener(DirectMediaTrackListener* aListener);
 
   // A disabled track has video replaced by black, and audio replaced by
   // silence.